1. Field of the Invention
The present disclosure relates generally for drive circuits for electrostrictive transducers, and more particularly, to drive circuits for piezoelectric actuators.
2. Description of the Background of the Invention
Drive circuits have been developed that are useful with piezoelectric actuators to cause the piezoelectric actuator to undertake useful work. Various methodologies have been utilized to cause the actuator to oscillate at a particular single frequency or range of frequencies. In addition, piezoelectric actuators can be designed to oscillate in a single or multiple bending modes.
A product sold by the assignee of the present application under the WISP® trademark dispenses a volatile liquid for air freshening purposes. The WISP® brand fragrance dispenser includes a piezoelectric actuator coupled to a curved plate having a plurality of small orifices extending therethrough. A volatile fragrance in fluid form is supplied in a refill container having a wick that transports the fragrance to the curved plate when the refill container is placed in the fragrance dispenser in an operative position. Electrical circuitry is provided to periodically operate the piezoelectric actuator and thereby cause emissions of fragrance droplets at a selectable emission frequency. Specifically, the electrical circuitry is responsive to the position of a switch to develop a series of emission sequences wherein consecutive emission sequences are separated from one another in time by a period that is dependent upon the switch position. The electrical circuitry includes an application specific integrated circuit (ASIC) that develops a drive voltage for the piezoelectric actuator wherein the drive voltage is ramped up and down in frequency during each emission sequence between preselected frequency limits. This approach is utilized to take into account that fact that it is desirable to drive the piezoelectric actuator at one of the resonant frequencies thereof for at least a portion of the emission sequence so that adequate atomization is achieved and due to the fact that the resonant frequencies vary from actuator to actuator. The need to sweep the drive voltage across a band of frequencies results in increased electrical requirements.